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Full text of "Handbook Of Chemical Engineering - I"

210
CHEMICAL ENGINEERING
Then
Ax = Weight of finished size in original feed, By = Weight of finished size in classifier sands, C(x — y) = Weight of finished size in mill discharge, and Dx = Weight of finished size in classifier overflow.
As before, the .weight of finished size in the material going to the classifier will equal the weight of finished size in the classifier products, so
or
C(x + y) = By + Dx
__ (D -C)
y' - (C - B) *
The ratio of circulating load (R) to original feed would be
A ~ ~T~ "     ^ lc  ~ x ^ (C - B)
Example 4.—As an illustration, suppose the figures are the same as in Example (1) except the percentage of undersize in the tube-mill discharge.
—65 mesh in the original feed......
—65 mesh in the classifier sands
-65 mesh in the mill discharge.....
—65 mesh in the classifier overflow. Substituting in the equation, R = 1.87.
PER CENT 38.0 27.8 59.4 87.0
Properly speaking, the circulating load is that part of the load which circulates, or returns to the starting point. In the case of the feed going direct to the ball mill, the circulating load is made up of the classifier sands only, as that is the only part of the original feed which completes the cycle. Following this concept, the ratio (R)
Y                        Y
of circulating load to original feed would be R - — instead of 1-----.
x                           x
HORSEPOWER REQUIRED PER FOOT OF MILL LENGTH
Internal	Proportion of mill volume occupied by charge					
diameter						
of mill,						
feet	0.1	0.2	0.3	0.4	0.5	0.6
1	0.0023	0.0099	0.022	0.042	0.065	0.093
2	0.0255	0.1100	0.254	0.460	0.730	1.040
3	0.1087	0.4630	1.070	1.940	3.070	4.380
4	0.288	1.2400	2.870	5.220	8.250	11.780
5	0.640	2.7200	6.290	11.430	18.070	25 . 740
6	1.200	5.1600	11.880	21.470	34.140	48.690
7	2.060	8.8500	20.430	37.060	58.610	83.530
8	3.260	14.1200	32.540	59.080	93.460	133.320
9	4,960	21.3200	49.090	89.310	141.240	201.330
10	7.130	30.8100	71.060	129.000	204.070	291.100
					1	
In this table the mill is assumed to be operating at the most efficient speed, as shown in the following table, and the charge is assumed to weigh 325 Ib. per cubic foot.